This invention relates to an improved injection blow molder wherein duplex molding of resin parisons with base or bottom parts and their stretching and blow molding into hollow molded articles can be accomplished continuously.
When an injection molded resin parison with a bottom part is put, on a core, in a blowing mold for blowing air from the core to produce a hollow molded article, it is not, technically, too difficult to form a double layer parison with a bottom and blow mold it, since the core may be used as a transferring member for such a parison. However, in a method for producing a hollow molded article wherein the injection molded parison with a bottom is heated and stretched, the core used in the injection molding can be utilized in the primary molding of a duplex parison with a bottom, but it may not be utilized in a secondary molding without modification since the parison with a bottom is clamped by a neck mold to be transferred. Further, every time the intermittent rotation of the injection molder is interrupted, each process such as injection, heating, stretching and blowing, and mold releasing must be performed. It is impossible to perform the process of the injection molding stage alone in a different molding cycle. Therefore, an injection molder of the type wherein the neck mold is transferred with a parison having a bottom by an intermittently rotated transferring platen is not considered suitable for producing double-layered hollow articles.
However, an injection molder considered structurally inappropriate may still be utilized for producing a duplex hollow article by the blowing method if a duplex injection molder of a parison with a bottom is inserted in the molding cycle from the stages of injection molding to mold releasing.
Thus, the first injection molder proposed was of the so-called four-stage, four-neck mold type in which are disposed four operation stages, that is, an injection molding stage, a heating stage, a stretching and blow molding stage, and a mold releasing stage. In this type of injection molder, a transfer platen intermittently rotates around a support shaft and, in the order mentioned, stops to perform the appropriate process when the neck mold is located at each stage. In order to produce a duplex parison with a bottom using an injection molder of such a structure, a cold parison, injection molded in advance, is attached to the core as an inner parison, and then an outer parison must be injection molded outside the inner parison. However, a special means is needed for attaching the cold parison to the core. In addition, if a hollow duplex molded article of superior quality is required, molten material should not be applied to a cold parison.